Balsa USA Enforcer - RC Groups
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Dec 02, 2009, 10:07 PM
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RyanPSU21's Avatar

Balsa USA Enforcer

I got a BalsaUSA Enforcer kit tonight to do as an electric conversion.

I'm going to power with a Turnigy something or other and 10S A123's. I'm going to join the 1000watt club finally with this one. I'm going to add mechanical retracts most likely Robart.
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Dec 03, 2009, 03:37 PM
D.W. Schmidt

I'd love to see some updates/pictures as you move along. I had considered this same plane a few years ago.

Dec 03, 2009, 06:40 PM
Colonel's Flying Aces
CeeJay047's Avatar
Originally Posted by RyanPSU21
I got a BalsaUSA Enforcer kit tonight to do as an electric conversion.

I'm going to power with a Turnigy something or other and 10S A123's. I'm going to join the 1000watt club finally with this one. I'm going to add mechanical retracts most likely Robart.

Flew one of those (nitro) a couple decades ago - VERY agile performer.
Be sure to keep the main gear short and the nose long - it needs considerable
angle of attack to break ground.
Dec 03, 2009, 09:00 PM
Registered User
RyanPSU21's Avatar
I will post some pictures when I get started which will most likely be this weekend. I've so far just gone for a skim through the manual and plans.

Thanks for the advice about the gear. I will make sure to maintain the ground angle. I will most likely go with a bigger nose wheel then called for since 2incher's don't tend to agree with grass all that well.
Dec 06, 2009, 04:51 AM
Xtreme Nut
I had one built for me but I sold her because I could not do the conversion with ease, esp the part of battery storage and access. Mine was built as a glow plane. Would love to see what you do with yours.
Dec 06, 2009, 10:43 PM
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RyanPSU21's Avatar
I got started this weekend. I picked up the retracts from the LHS. Going to use a Robart .60size mechanical for the nose and GreatPlanes .60 size mechanicals for the mains. I would use Robart for all 3 except that the Robart .60 size mechanicals are only available with 3/16 struts instead of 5/32 which is a bit overkill.

I started on the fuselage mostly following the plans. I truely dread/hate plywood fuselage sides combined with longerons stuck to them. This combines to make something next to impossible to flex. I debated cutting new fuselage sides out of balsa and didn't. Everything went well until trying to pull the nose together. My tape and pins kept popping off so I attempted to hold it together while glue sets. In short I ended up with a twisted abomination of a nose so I scrapped the whole thing, ripped everything off one fuselage side so I could use it as a pattern and started over with balsa as I should have done to start with. As a note, in the manual it tells use to put the rear formers together along with the firewall and then apply thick CA when all is held together. If you do this you will have a very weak firewall adhesion since you can't really get glue under the trystock there. Consequently the firewall popped right off so I could easily re-use it. Fortunately I hadn't trashed the scrap sheets yet the formers came out of so I traced off the missing part outline to make new ones.

The nose of this thing doesn't really serve any purpose other then the final appearance of the plane. The nose gear is mounted to the wing. When I made the balsa fuse sides on the second try I only used 1/8x1/4 instead of 1/4x1/4 for the longerons going forward of the wing saddle. This makes for a much more flexible and easier to work with front fuselage.

I don't really see a point to making the wing bolt on for this plane. It's not really going to make transportation much easier. The nose only sticks about a foot past the leading edge of the wing. I am going to build this with 1 piece. This will work out better for my plans for a hatch and battery storage.

Because I'm making it one piece, it leaves the option open now to make the entire fuselage top hatch instead of just the cockpit window. For aligning the fuselage and keeping it square it will be much easier to do with the fuselage upside down since the top is flat. I chopped off the top of the fuselage formers. Because the wing is going to be permanently attached there is no reason for former F4 to be plywood so it got cut out of balsa. I cut holes in the formers to start with and after cutting the tops off some of them didn't have enough structure so I put some 1/8x1/4 pieces in for some temporary support.

This time with balsa and no ply and upside down it went together much easier and was easy to pin down and support to glue. The firewall was epoxied in properly this time as well. When pulling the nose together at the front former. You will need to add some bits of wood here to get any kind of glue joint to hold. With plywood this was near impossible. With balsa fuse sides some little 1/4x1/4 bits worked okay. Put them in before untaping or otherwise unclamping. 1/8 inch balsa former just isn't enough to hold the force of it trying to open.

I am looking at how exactly the nosegear will work. If it retracts rearward it will have to go through some of the wing structure. The main spar will I think be behind where the wheel will be. If it retracts forward the linkage for retraction gets more complicated. I think to make these work the ground plane will have to be moved up 1/2inch to 3/4inch to make the wheels fit. The main gear may have to be widened a little bit also. I haven't dug too deep into this issue yet beyond some skimming of the plans.

I am also planning on moving the aileron servo back to 2 servos at the surfaces instead of at the center with nyrods.
Dec 09, 2009, 02:39 AM
Registered User
Hi guys,

My dad and I have been doing electric Force One and Enforcer models for years. We currently have:

1. Force One with Jeti Phasor 45/3 on 5S with 10X7 APC prop. Been flying for about 5 years and has hundreds of flights.

2. Enforcer converted to 90MM EDF with Wemo Midi Pro, Hacker B50-13XL on 8S

3. Force Once with Storm 70 EDF on 4S (done but the motor is a Christmas present so it won't fly until 12/25/09)

4. Scratch design based upon the Force One that is a little smaller than the Enforcer and has Spring Air Retracts, Wemo Mini Pro, Hoffman electrics Beast on 4S. Should fly within the next week or so.

These are excellent platforms. Reasonably fast and easy to fly. Do a search and I think there is a picture posted here of my Force One with the Jeti at one of the Mid Winter Electric fly ins in San Diego.

Dec 09, 2009, 10:09 PM
Registered User
RyanPSU21's Avatar

What was your flying weight and how many watts were you pulling on the 90mm EDF Enforcer?

I made the fuselage hatch framework. I need to make an LHS trip to get some 1/64" play to use instead of the called for 1/32" for the fuselage top back and front. 1/64" will be much easier to bend around the top curve, not to mention some more weight save.

In the meantime I did a little start to the wing tonight. You can see from the picture that this wing presents some definete building board size challenge. I am going to attempt to build it with the front of the ribs hanging off the board. Looking at the construction step this really shouldn't be a problem for keeping everything straight.
Dec 09, 2009, 11:28 PM
Registered User

Right at about 7 pounds on 1000 square inches of wing area. The watts should be about 1200 or so on older batteries. Maybe a couple hundred more on newer packs. It is a lightly loaded pussy cat. My only regret was we didn't put retracts on it.

I have seen the Enforcer converted to turbine power, I think it would easily handle a 100-120MM fan and batteries.

Dec 20, 2009, 09:40 PM
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RyanPSU21's Avatar
I haven't posted much but quite a bit more has been done. The fuselage is close to finished except for finishing up the hatch. The bottom sheeting is on the wing and I've got the retract locations planned and just need to trim the ply doublers a bit for the rails. I've got the nosegear location planned. I'm going to mount the nose gear to retract forward into the nose. Looking at the CG I don't think the battery will need to go that far forward so that aren't doesn't need to be preserved for battery space.

I ordered the motor for this tonight. Found an AXI 4130/20 on closeout somewhere for a decent price.

There really is no bargain out there for speedcontrols that will handle 10S Voltage. I'm going to go with a Castle Creations Phoenix ICE 50amp 33volt. Turnigy controllers and anything else from hobbyking cost nearly as much.

The ESC's aren't available anywhere at the moment but I don't need the ESC until March or so much later on in construction.

I did some work on moto-calc and came up with the following for the motor/battery/prop combo. Going to go with something around a 14x12 APCe prop.

Motor: Model Motors AXI AC4130/20; 305rpm/V; 1.2A no-load; 0.099 Ohms.
Battery: A123 ANR26650 M1 (30C); 10 cells; 2300mAh @ 3.3V; 0.016 Ohms/cell.
Speed Control: Castle Creations Phoenix 80; 0.001 Ohms; High rate.
Drive System: 14x12 APC Prop; 14x12 (Pconst=1.17; Tconst=1) direct drive.
Airframe: Enforcer;; 113.3oz RTF; 15.1oz/sq.ft; Cd=0.033; Cl=0; Clopt=0.29; Clmax=0.8.
Stats: 126 W/lb in; 100 W/lb out; 22mph stall; 37mph opt @ 51% (24:23, 91F); 1996ft/min @ 37.9; -590ft/min @ -10.5.


MotoCalc was unable to determine a throttle setting for hands-off cruise airspeed, so the best lift-to-drag ratio airspeed and throttle setting will be used instead.
Inability to determine a throttle setting for an airspeed usually means the model is not capable of reaching the required speed with the given power system, or the airfoil information has not been specified correctly.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (32.8A) falls approximately between the motor's maximum efficiency current (18.3A) and its current at theoretical maximum output (140.6A), thus making effective use of the motor.
The voltage (27.8V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Possible Aerodynamic Problems:

The static pitch speed (79mph) is greater than 3 times the stall speed (22mph), which might make take-off or hand launching difficult, and is inefficient in flight unless high speeds are intended.
Pitch speed can be decreased by using a lower pitched and/or larger diameter propeller, a higher gear ratio, a lower cell count, or some combination of these methods.
The diameter (14.0in) to pitch (12.0in) ratio is less than 1.5:1, which will result in reduced propeller efficiency at low speeds (the propeller is stalled). Although this is not likely to affect flying characteristics, it may make take-off or hand launching difficult.

Aerodynamic Notes:

With a wing loading of 15.1oz/sq.ft, a model of this size will have very sedate flying characteristics. It will be suitable for relaxed flying, in calm or very light wind conditions.
The static thrust (110.4oz) to weight (113.3oz) ratio is 0.97:1, which will result in very short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and steep climb-outs.
At the best lift-to-drag ratio airspeed, the excess-thrust (73.2oz) to weight (113.3oz) ratio is 0.65:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.

General Notes:

This analysis is based on calculations that take motor heating effects into account.
These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.
Dec 27, 2009, 03:31 PM
Registered User
RyanPSU21's Avatar
I've gotten quite a bit done in the last few days. The wing is now 99% completed. Just some small miscelaneous things left to do here and there on it. Next in line will be hooking up the main gear retracts and getting them to work. After that will be mounting the fuselage and trying to see if I can get the nose gear going off the same servo or not. Hopefully I can. I have the motor for this on hand now and ordered a mount from Esprit Model for it. I think after getting the motor mount worked out I will build some kind of shroud or cowling to cover the motor. The plane has really clean lines overall and I don't want to wreck the appearance with the motor and a not that attractive mount hanging off the back. There is about 2 inches between the front of the motor and firewall so there will be a substantial gap there if I do nothing. I need the mount right now to do anything more on the fuselage. I need to get the firewall drilled and setup before I can join it to the wing.

Weight wise this thing should be going well. The AXI 4130 is only about half the weight of a .60 glow motor. The battery brings the power system up to overall a little higher. My fuselage weight saves should make up for the added retract weight. I should be able to come out with a plane only a few ounces heavier then what a glow version would have. Not including that the glow version would be carrying 12-16ounces of fuel at takeoff that is never considered in their weight. With that in mind I should be equal or less then takeoff weight for a fuel powered version.

I'm going on vacation to visit my parents for a week tomorrow so no more work on this until I get back. The motor mount should be here by then waiting so full speed ahead once I get back.
Dec 27, 2009, 03:49 PM
Is it Friday yet?
DropTank's Avatar
Looking good! I built one of those years ago. It was a great flying plane. I had radio interference and the plane rolled upside down and nosed into the soft plowed field. I walked over to pick it up and the engine was still running. It looked like a yard dart sticking in the ground. I recovered the front of the fuse and put it in the air again.
Dec 30, 2009, 11:53 PM
jodini's Avatar
This I got to see! I love flying my buddies enforcer, but I think an electric version would be awesome!

Keep up the good work!
Dec 31, 2009, 08:19 PM
Registered User
Ed Couch's Avatar
Here are a couple of my electric enforcer based airframes. The single seater was lost a couple seasons back due to bad case of dumb thumbs and out of trim airframe. The twice seater flies just over a hundred miles an hour and is a blast. Based off the Ivan Schomer update for ducted fan. Hacker powered but waiting future update before flying again. Very sweet flying vehicle. ed
Last edited by Ed Couch; Dec 31, 2009 at 08:25 PM.
Jan 06, 2010, 07:39 AM
Registered User
RyanPSU21's Avatar
Thanks for the pics Ed. Your 2 look really great. I would love to do mine as an EDF also except that I've never flown an EDF before and need something with enough oomph to get off grass. The first making this not a great idea to make EDF, the second would turn this into a cost prohibitive project right now.

I really like what you did with the cockpit look. Nice change over what the kit looks like. Do you have anymore details on the canard? How much surface area does it have? It is just a normal control surface or is it flying?

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